This invention relates generally to gate valves and more particularly to an improved valve seat structure for gate valves of the type having a slab gate member and cooperating seat members which form a seal both upstream and downstream.
Slab gate valves typically employ a slab gate element which is provided with parallel planar sealing faces for sealing against annular seat members disposed on both the upstream and downstream sides of the gate in surrounding relation to the flow passage through the valve. For facilitating the establishment of a fluid-tight seal between the gate and seat member, it has been common practice to provide the sealing face of the seat member with an annular ring insert of resilient or plastic deformable material such as Teflon. Unfortunately, fluoroelastomers such as Teflon have very little abrasion resistance and accordingly, the sealing capability of the fluoroelastomer sealing insert deteriorates after repeated use. The diminution of sealing ability is also noted with most other resilient sealing inserts due to the effects of erosion. If the valve is operating in sandy slurry media or other similar abrasive or corrosive ladings, the problem tends to become a critical one in a very short time.
Another problem which tends to occur in very high pressure applications is the frequent loss of the annular sealing element by its being pressure extruded from the face of the seat ring.
It is therefore a primary object of this invention to provide a valve seat assembly for a gate valve which comprises a seat ring having a sealing insert in the front face thereof which has enhanced resistance to abrasion.
It is another object to provide a valve seat assembly for a gate valve which comprises a valve seat ring which can be used as either an upstream or downstream seat and comprises a valve seat ring with an annular sealing element in the face thereof which is resistant to being pressure extruded from the seat ring.
A further object is to provide an improved valve seat assembly for a gate valve which comprises a seat ring with an annular sealing element in the front face thereof which tends to be fluid pressure energized for enhancing the sealing capabilities of the valve seat.